What is Naegele's rule?

Due date = LMP + 280 days. We adjust for cycle length: add (cycle − 28) days for longer or shorter cycles.

How accurate is the due date?

Only ~5% of babies arrive on their due date. Most arrive within two weeks of it — full term is 37–42 weeks.

IVF conception date is known precisely, so we use transfer date + 266 days (or 263 for 3-day embryos) rather than relying on LMP.

Naegele's rule assumes a 28-day cycle. For irregular cycles, an early ultrasound (8–13 weeks) gives the most accurate due date.

No — this is informational. Your obstetrician will confirm your due date based on clinical assessment and ultrasound.

Estimated due date via Naegele's rule or IVF/ultrasound.

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Follow these steps — everything happens instantly in your browser.

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Step 1. Pick a calculation method: last period, IVF transfer or ultrasound date.
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Step 2. Enter the relevant date.
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Step 3. If using last period, enter your cycle length.
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Step 4. Read the estimated due date, gestational age and trimester.

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